We have developed a powered ankle-foot orthosis that can assist human walking. The ankle-foot orthosis has an artificial pneumatic muscle providing plantar flexor torque in response to soleus muscle activation (i.e. proportional myoelectric control). We focus on robotic assistance for the ankle because plantar flexion during stance is a major source of mechanical power during walking and is directly related to walking ability in individuals with neurological disability. Neurologically intact subjects wearing the orthoses rapidly adapt their muscle activation patterns to compensate for the added mechanical power provided by the orthoses. We propose to determine if subjects with incomplete spinal cord injury benefit from practice walking with the powered orthoses. Our preliminary data suggest that proportional myoelectric control provides a powerful stimulus for re-shaping muscle activation patterns in subjects with incomplete spinal cord injury. The orthosis effectively makes the muscle stronger. This provides the nervous system with enhanced proprioceptive feedback linking muscle recruitment to joint motion. This innovative approach is unique as other robotic rehabilitation devices rely on an external agent (i.e. a computer) to control the timing and magnitude of mechanical assistance rather than the patient's own nervous system as we propose. We will measure H-reflexes, electromyography, kinematics, kinetics, and metabolic cost in individuals with incomplete spinal cord injury before and after eight weeks of practice walking with the orthoses. The results will provide sufficient data to design an extended randomized clinical trial of the powered orthosis. PUBLIC HEALTH RELEVANCE: We will study people with incomplete spinal cord injury walking with robotic braces on their legs to determine if the braces can improve their walking ability. The results may lead to new robotic therapies for improving rehabilitation after spinal cord injury or stroke.